Motor vehicle tyre, particularly for lorries and the like

ABSTRACT

A vehicle wheel tire includes a carcass structure, a belt structure, and a tread. The tread includes four circumferential grooves and a plurality of transverse grooves that define at least five circumferential rows of blocks, each block approximating a polygon. The longitudinal sides of the blocks are inclined in the same direction at a predetermined angle to the equatorial plane of the tire. The blocks of each row are circumferentially staggered relative to the blocks of the next row. The blocks of the central row include stiffening means. Profiles of the front sides of the blocks of the central row are the same as the profiles of the rear of the blocks of the central row rotated through 180°. The blocks of the shoulder rows are elastically linked to the blocks of the intermediate rows.

[0001] The present invention relates to motor vehicle tires,particularly for lorries and the like, intended for heavy-haulage.

[0002] The invention is particularly concerned with tires intended foruse on the live axle of trucks or articulated lorries on mid-lengthjourneys, i.e. on routes which, as is well known, impose severer demandsand generate more wear than long journeys, which generally take place onmotorways.

[0003] Tyres designed to be mounted on live axles usually have a treadof elastomeric material containing a relief pattern comprisingcircumferential grooves intersected by transverse grooves so as to forma plurality of blocks, hence the name “block” tires, to distinguish themfrom “ribbed” tires formed from continuous circumferential ribs havingpoorer grip properties.

[0004] In the remainder of the description and in the claims thatfollow, the expression “elastomeric material” is used to indicate therubber compound in its entirety, that is the total mixture composed ofone or more base polymers suitably amalgamated with reinforcing fillersand other product additives and process additives such as accelerators,retardants, anti-ageing agents, plasticizers, cross-linking agents andso forth.

[0005] Furthermore, the term “tread” is used to indicate the strip ofelastomeric material provided with a sheet of a different compound laidon the radially innermost surface of the said strip to promote theadhesion of the tread when cold to the underlying elements of thecarcass, in particular the belt layers.

[0006] Tyres for live axles have to satisfy multiple requirements: inparticular they must provide good grip on both dry surfaces and wetand/or snow-covered surfaces.

[0007] In addition, both the market and many national legislations areincreasingly demanding quiet-running tires, whereas the use of “block”tires generally produces more noise than “ribbed” tires.

[0008] The tread must also wear evenly and offer high mileage.

[0009] On top of this, treads are required to have a pattern capable ofefficiently expelling stones and small fragments that become trapped inthe grooves of the tread, since if such stones or fragments were toremain in the tread they could perforate the tread as the tire wearsdown and so damage the underlying belt structure.

[0010] The prior art already includes tires capable of confronting theseproblems and offering a solution to them.

[0011] For example, Italian Patent 1,245,773 by the Applicant disclosesa tread comprising at least four rows of blocks defined by at leastthree circumferential grooves of different widths, the axially innermostgroove being wider and the two lateral grooves on either side of theequatorial plane of the tire being narrower, and by a plurality ofoblique transverse grooves connecting pairs of circumferentiallyadjacent grooves.

[0012] In this solution the narrow groove that separates the two lateralrows of blocks on each half of the tire is characterized by the factthat its width is no greater than 2.5 mm and its depth not greater thanthat of the confluent transverse grooves while the blocks of the twolateral rows are circumferentially staggered relative to each other sothat every block of each row is next to two consecutive blocks of theadjacent row.

[0013] This patent describes other solutions comprising, for example,two additional axially internal circumferential grooves defining a pairof circumferential ribs, in the walls of which there are obliquetransverse grooves extending as far as the equatorial plane, so that theribs have the appearance of two adjacent rows of blocks.

[0014] The blocks of all rows have an ordered configuration, thelongitudinal sides of the blocks of any one row lying along two linesparallel to the equatorial plane.

[0015] In another solution the two rows of blocks of the two centralribs can be joined together to form a single row straddling theequatorial plane and in another solution the blocks of the central rowmay be of roughly hexagonal shapes.

[0016] Also known is a tire comprising a “block”-type tread composed offour, that is two lateral and two central, circumferential grooves ofequal width, and a plurality of transverse grooves that together definefive rows of blocks, that is two axially external shoulder rows, twoaxially internal intermediate rows and a central row of blocks passingthrough the equatorial plane of the tire.

[0017] The blocks of the central row and of the intermediate rows areall of identical “Z” shapes defined by two longitudinal sides and twotransverse end sides, while the shoulder blocks are defined by twolongitudinal sides and two transverse end sides, one at the front andone at the rear, both in the form of arrows and complementary to eachother.

[0018] The longitudinal sides of the blocks of all rows are parallelwith each other and inclined to the equatorial plane while thetransverse end sides of the blocks of the central and intermediate rowsare parallel with each other and slightly inclined to a planeperpendicular to the equatorial plane.

[0019] The blocks of the adjacent rows are also circumferentially offsetrelative to each other.

[0020] The Applicant was convinced that the performance of tires of theprior art with “block”-type treads could be improved, particularly asregards protection against the penetration of stones towards the belt inthe central zone of the tread, which is usually at greater risk, withoutthis improvement triggering negative changes to other characteristicssuch as resistance to stone penetration in the lateral zones of thetread, grip, wear resistance and quiet running, but instead if possibleintroducing further improvements.

[0021] It was thought that it would be possible to achieve this resultby employing a “block”-type tread comprising a widening of the centralcircumferential grooves disposed between the central row and theintermediate rows of blocks while nonetheless maintaining the width ofthe lateral circumferential grooves within the range of a predeterminedvalue that would still be useful in protecting against the penetrationby stones.

[0022] It was realized that the accomplishment of this task could dependon achieving a particular ratio between the widths of thecircumferential, lateral and central grooves.

[0023] It was then felt that although the reduction in the width of theblocks of the intermediate rows, necessary to permit both widening ofthe central grooves and a predetermined width of the lateral grooves,would introduce a consequent poorer rigidity of the intermediate blocks,this effect could be compensated for by increasing the rigidity of theblocks of the central rows and by providing an elastic linkage betweenthe blocks of the shoulder and intermediate rows.

[0024] The idea, in fact, was to liken the central, intermediate andshoulder rows of blocks to three parallel springs under load so that bygiving the blocks of the central rows a more rigid shape than that ofthe other blocks it was possible to create in the central spring agreater elastic reaction which would protect the other rows of blocks.

[0025] It was also felt that it should be possible to reinforce theresistance to bending deformations of the intermediate and shoulder rowsby means of a mutual elastic linkage so that these rows in combinationcould present an increased resistance to bending deformations.

[0026] In order to achieve satisfactorily quiet running thecharacteristics of inclining all the longitudinal sides of the blocks tothe equatorial plane, and the circumferential staggering of the blocksof one row relative to the next, have been maintained.

[0027] In an initial aspect the invention therefore relates to a vehiclewheel tire comprising a carcass structure that includes a central crownportion and two sidewalls terminating in two beads for fixing the tireto a wheel rim; a belt structure coaxially fixed to the carcassstructure; and a tread extending coaxially around the belt structure,its thickness being defined between the outer surface intended tocontact the ground and the inner surface in contact with the said beltstructure, having a tread pattern which comprises four, that is twolateral and two central, continuous circumferential grooves and aplurality of transverse grooves that together define fivecircumferential rows of blocks, that is two axially external shoulderrows, two axially internal intermediate rows and a central row thatbasically straddles the equatorial plane of the tire, each block being apolygon composed of two sides extending longitudinally in acircumferential direction and two transverse end sides, one at the frontand one at the rear with reference to a direction of travel,characterized in that in the said tread pattern:

[0028] a) the longitudinal sides of the blocks of each row are inclinedin the same direction with a predetermined angle “α” to the equatorialplane of the tire,

[0029] b) the blocks of one row are circumferentially staggered relativeto the blocks of the next row,

[0030] c) the ratio of the width, measured axially, of each centralcircumferential groove to the width, measured axially, between oppositelongitudinal sides of the blocks of the central row is not less than20%,

[0031] d) the ratio of the width of the lateral circumferential grooveto the width of the central circumferential groove is between 45% and60%,

[0032] e) there are means of stiffening the blocks of the central rowconsisting in the fact that each front and rear side of each block isformed by a first and a second straight segment separated by anintermediate third connecting segment, the said first and secondsegments being inclined to the equatorial plane, and the profile of thefront side, rotated through 180°, being the same as that of the rearside, and

[0033] f) there are circumferential elastic means of linkage between theblocks of the shoulder and intermediate rows.

[0034] Conveniently, for the purposes of improved noise reduction, theinclination of said third segment is the opposite of that of the firstand second segments.

[0035] The elastic linkage means preferably consist in the presence ofelastomeric material of predetermined height between the bottom line ofthe axially external lateral groove and the inner boundary surface ofthe tread, and in an axially outer lateral groove whose width, measuredon the outer boundary surface of the tread, is at least 6.5 mm.

[0036] The tire conveniently comprises elastic linkage means between theadjacent blocks of the central row to contain the bending deformations;these elastic linkage means consist in the fact that, between pairs ofadjacent blocks along the relevant transverse groove, an elastomericrelief extends from the internal surface of the tread toward the outersurface up to a predetermined height, preferably equal to at least 15%of the thickness of the tread.

[0037] Also, in a preferred embodiment, the first and second segments ofboth front and rear sides of the central blocks are inclined in the samedirection by a predetermined angle “βo” relative to a planeperpendicular to the equatorial plane of the tire.

[0038] Preferably, the said angle “βo” is between 15° and 21°.

[0039] Still more preferably, in each central block the intermediatethird segment between the two straight segments forms an angle “γ” ofbetween 30° and 60° to a plane perpendicular to the equatorial plane.

[0040] The said constructions of the transverse end sides of the centralblocks advantageously improve the characteristics of quiet running andgrip.

[0041] In accordance with one particular embodiment the tire of theinvention comprises elastic linkage means between adjacent blocks of theshoulder rows.

[0042] These elastic linkage means preferably consist in the fact that,between pairs of adjacent blocks along the relevant transverse groove,an elastomeric relief extends from the internal surface of the treadtoward the outer surface up to a predetermined height.

[0043] The invention advantageously involves determining the height ofthis relief according as greater or less stiffness is required.

[0044] This relief can therefore vary between 9% and 60% of thethickness of the tread.

[0045] The tire with the pattern according to the invention may comprisestone expulsion means, preferably comprising a narrowing of the grooveson only one of the defining sides of the grooves.

[0046] In another preferred embodiment the tire comprises in apredetermined pitch of its pattern five transverse grooves, the distancebetween the centre lines of any two of the five transverse grooves beingapproximately ⅕ of the pitch.

[0047] However, the present invention will now be explained more clearlywith the aid of the following description and of the accompanyingfigures, which are provided purely by way of example without anylimitation being intended. In the figures:

[0048]FIG. 1 illustrates in a right cross section the general structureof a tire according to the invention;

[0049]FIG. 2 is a plan view of the tread pattern according to theinvention in one embodiment;

[0050]FIG. 3 shows a partial enlargement of FIG. 2;

[0051]FIG. 4 is a right cross section through the abovementioned patterntaken on the plane marked IV-IV in FIG. 3;

[0052]FIG. 5 is a right cross section through the abovementioned patterntaken on the plane marked V-V in FIG. 3;

[0053]FIG. 6a is a different right cross section through theabovementioned pattern taken on the planes marked VI-VI identified byletters A, B, C, D, E, F in FIG. 2;

[0054]FIG. 6b illustrates a variant of the pattern shown in FIG. 6a;

[0055]FIG. 7 is a right cross section through the abovementioned patterntaken on the plane marked VII-VII in FIG. 2;

[0056]FIG. 8 is a different right cross section through theabovementioned pattern taken on the plane marked VIII-VIII in FIG. 3;

[0057]FIG. 9 is a right cross section through the abovementioned patterntaken on the plane marked IX-IX in FIG. 3;

[0058]FIG. 10 illustrates the shape of a block belonging to the centralrow;

[0059]FIG. 11 illustrates a block from the central row superimposed on ablock from the intermediate row;

[0060]FIG. 12 illustrates a block from the intermediate row superimposedon a block from the shoulder row; and

[0061]FIG. 13 illustrates in a partial view from FIG. 2 the distributionof transverse grooves in one pitch of the pattern.

[0062]FIG. 1 illustrates a vehicle tire according to the invention, inparticular a tire, suitable for mid-length journeys, fitted to the drivewheel of a road train or truck.

[0063] The tire comprises a carcass 1, shaped into a toric ringpreferably consisting of a single reinforcing ply strengthened withmetal cords lying in radial planes, that is planes containing the axisof rotation of the tire. The edges of the ply are folded axially, fromthe inside towards the outside, around two annular metal cores 2,usually known as bead wires, constituting the reinforcement of thebeads, i.e. of the radially innermost edges of the said tire, theirfunction being to enable the tire to be fitted to its corresponding rim:this tire is mounted on a rim C of the channel type in which thesurfaces supporting the beads of the tire taper outwards at an angle oof approximately 15°.

[0064] On the crown of the said carcass there is laid a thick tread 3 ofelastomeric material, in which is produced a road-contact pattern inrelief designed to ensure among other things that the tire has qualitiesof grip, quiet running, draining capacity and evenness of wear.

[0065] The tread has a predetermined thickness and is defined betweenthe outer surface intended to contact the ground and the surfacetangential to the cords of the radially outermost belt layer, of whichmore later. This thickness usually includes a sheet of elastomericmaterial drawn for simplicity's sake in FIG. 1 as a solid line 3′. Thematerial of this sheet, applied hot to the tread, is different from thetread material, being expressly designed to produce adhesion at ambienttemperature between the elastomeric material of the tread and the tirecomponents lying radially beneath it.

[0066] The thickness of the sheet is normally between 0.3 and 1 mm,compared with a total thickness of the tread of the order of 20-25 mm.

[0067] Situated between the carcass and the tread is an annularreinforcing structure 4, usually known as the belt, which iscircumferentially inextensible and comprises at least two radiallysuperimposed layers (4 a, 4 b) of rubberized fabric provided with metalreinforcing cords. These cords are arranged parallel with each otherwithin each layer but cross at angles relative to the cords of theadjacent layer, preferably in a symmetrical arrangement relative to theequatorial plane of the tire. There is preferably also a third layer 4 cof metal cords of high-elongation type wound circumferentially, in aradially outer position, at least around the edges of the abovementionedunderlying layers: as is well known, this structure has the specificpurpose of counteracting the forces acting in the tire during use,related to inflation pressure and centrifugal force, as well as ofensuring the necessary steering behaviour properties, specificallyduring cornering.

[0068] The tread comprises (FIG. 2) four continuous circumferentialgrooves, two of which are central 5 and two lateral 6, and a pluralityof transverse grooves that together define five circumferential rows ofblocks, that is two axially external lateral shoulder rows, two axiallyinternal intermediate rows and a central row.

[0069] Going into more detail, the pattern consists of two pairs oflateral rows of blocks, namely blocks 7 in the intermediate rows andblocks 8 in the shoulder rows and a central row of blocks 9 passingaround the equatorial plane X-X; the two lateral rows of each pair aresituated on either side of the equatorial plane X-X.

[0070] The blocks of the intermediate and shoulder rows are defined bytransverse grooves 10 and 11 respectively and the blocks of the centralrow by transverse grooves 12.

[0071] Each block in all the various possible embodiments comprises foursides and corresponding vertices a, b, c, d.

[0072] More specifically, each block is defined by two longitudinalsides oriented substantially circumferentially and two transverse endsides, one at the front and one at the rear with reference to adirection of travel. For convenience in FIG. 2 the vertices to the leftof the equatorial plane have been identified at the junctions betweenthe extensions of two sides, although the preferred embodiment comprisescurvilinear connecting segments between sides leading to a vertex, asdepicted to the right of the equatorial plane.

[0073] The blocks can assume many different polygonal configurationsprovided that, having defined a direction of travel of the tire, forexample the direction of the arrow “W” in FIG. 2, it is possible todefine relative to this direction, for each block, a pair of frontvertices a, b and a pair of rear vertices c, d.

[0074] Although the invention is suitable for many different shapes ofblocks, it has been found convenient, for the purposes of satisfactorymoulding of the tread pattern, to adopt blocks of essentiallyrectangular, quadrilateral or indeed rhomboidal polygonal shape, oroptionally with certain modifications to certain parts, for the blocksof the intermediate and shoulder rows, as an examination of FIGS. 2 and3 clearly shows.

[0075] In addition, in the embodiment shown in FIG. 3, each block 7 ofthe intermediate rows has its front side 13 between vertices a and baxially staggered by a predetermined amount “Do” relative to the rearside 14 between vertices c and d of the neighbouring block preceding itin the same row.

[0076] In FIG. 2, to the left of the equatorial plane, the frontportions of the sides 15 have been drawn in dashes because, as willbecome clearer later, the block in the preferred embodiment is definedby the upper portion of this side drawn with a solid line.

[0077] Additionally, sides 15 and 16 of the blocks extending between afront vertex a, b and a rear vertex c, d are parallel to each other andinclined at a predetermined angle “α” to the equatorial plane markedX-X.

[0078] In essence the construction of the blocks 7 and their arrangementin the intermediate lateral rows is such that the front and rear sidesof neighbouring blocks defining the transverse grooves 10 are directlyopposite each other (FIG. 3) only along a segment “1” of their length.

[0079] Also, in a preferred embodiment, all the vertices of the blocks 7of the intermediate rows, which are arranged identically for each block,are aligned along lines parallel to the equatorial plane.

[0080] The blocks 8 of the shoulder rows preferably have verticesaligned on two lines parallel to the equatorial plane, one of whichlines is aligned with the edge of the pattern, and the shape of theseblocks is still more preferably combined with the preferredcharacteristics of shape and arrangement of the adjacent blocks 7 of theintermediate rows so as to form lateral circumferential grooves 6 ofconstant breadth.

[0081] The embodiment of the blocks 7 of the intermediate rows is thatdefined by the sides drawn in solid lines in FIGS. 2 and 3. As thesefigures show, the offset between the sides 15 of two consecutive blocksof the row 7, measured perpendicularly to these sides, is equal to “D1”.

[0082] As is visible in FIG. 3, the portions of the blocks 8 of theshoulder rows alongside the blocks 7 of the intermediate rows comprisetwo straight segments 8′ and 8″, parallel and inclined to the equatorialplane by the predetermined angle “α”, and an intermediate connectingsegment 8′″.

[0083] In this configuration one of the two straight segments 8′, 8″ isstaggered relative to the other by the quantity “D1” equal to the offsetbetween upper and lower base sides of two blocks 7 arranged one afterthe other in the intermediate row.

[0084] Since, as can be seen in FIG. 3, one of the sides of the block 8of the shoulder row is separated from the adjacent block 7 of theintermediate row by the same quantity “D1” by which the preceding blockis set back in the same row, the result is a lateral groove 6 ofconstant breadth between the adjacent blocks.

[0085] Advantageously the formation of circumferential lateral grooves 5and 6 of constant breadth avoids the presence of narrowings of sectionin the circumferential direction, which is good for water drainage inthe contact patch, thus improving grip in the wet.

[0086] Preferably, as can be seen in FIG. 3, the intermediate segment8′″ between the two straight segments forms in each block a recess whichcontinues the transverse groove 10.

[0087] Advantageously the formation of the said recess into the blocksof the shoulder row increases the tractive capacity of the tire at thevery portions of the tread best suited to providing this characteristic.

[0088] Another characteristic of this tread is that the sides of theblocks of one row are circumferentially offset relative to the blocks ofthe adjacent row in such a way that each block 8 of the shoulder row isnext to at least two blocks 7 of the intermediate row. Thecircumferential lengths of the offset may be derived from blocks lyingside by side for approximately ⅓ of the length of the adjacent block oreven lying alongside each other for lengths greater than the previouslength.

[0089] In the version shown in FIG. 2, the blocks 9 of the central roware staggered circumferentially relative to the blocks 7 of theintermediate rows and each central block lies alongside two blocks ofthese intermediate rows. Furthermore, those sides of the blocks of thecentral row that connect an upper vertex with a lower vertex areparallel to each other and inclined by the predetermined angle “α” tothe equatorial plane.

[0090] Advantageously, the various characteristics, namely theinclination of the sides of the blocks by an angle “α” to the equatorialplane, the offset between the two base sides in the blocks of the innerlateral rows, and the circumferential stagger, produce, in combinationwith each other, better performance in terms of grip in both dry and wetconditions, together with low noise.

[0091] Still another characteristic form of the invention is representedby the fact that the pattern includes elastic means of linkage betweenthe blocks 7 of the intermediate rows and the blocks 8 of the shoulderrows.

[0092] These linkage means consist (FIGS. 5, 6) in the presence ofelastomeric material of predetermined height “h” between the bottom lineof the circumferential grooves 6 and the inner boundary surface 3′ ofthe tread. The circumferential grooves 6 each have a width measured onthe outer boundary surface of the tread of between 6.5 and 8.5 mm.

[0093] This predetermined height “h” is at least 1 mm and may be up to 5mm. The value “h” is preferably between 4% and 24% of the thickness ofthe tread.

[0094] This characteristic is advantageous for the purposes of evenwear, because, beneath the contact patch, the blocks 7 of theintermediate rows, which are subject to forces directed basically in therolling direction, are protected against substantial bendingdeformations by the presence of the elastomeric layer joining theseblocks to those of the shoulder 8.

[0095] In practice, with the abovementioned stresses the blocks 7 and 8of the intermediate and shoulder rows, joined by a layer of rubber andseparated by a longitudinal groove of reduced width, offer, incombination, greater resistance to the deformations than would be thecase if the layer of height “h” were missing.

[0096] Also, because of the resistance to bending deformations the rowof shoulder blocks experiences even wear.

[0097] The geometrical shape of the blocks 9 of the central rowconstitutes another characteristic of the invention.

[0098] Returning to FIG. 2, it can readily be seen that the vertices ofthe blocks of the central row 9 are so arranged as to give rise to ablock of chunky shape which is very effective at resisting tearing andlaceration. The shape of the blocks of the central row is combined withthe characteristics of shape and position of the neighbouring blocks 7of the intermediate rows to produce circumferential grooves 5 ofconstant breadth.

[0099] This configuration is achieved by the fact that each block 9 inthe central row is formed, in the portions facing the blocks of theadjacent rows, by two straight parallel segments 17, 18 inclined to theequatorial plane by the angle “α” and by an intermediate connectingsegment 19 inclined to the equatorial plane in the opposite direction to“α” by an angle of different amplitude.

[0100] It should be observed that the two intermediate segments 19produce an offset of the two segments 17 with respect to the segments 18by a distance such as to create lateral grooves 5 of constant breadthbetween adjacent blocks.

[0101] Each block 9 comprises front and rear sides formed in aparticular way. Thus, as is clearly shown in FIG. 3, each front side ofthese blocks 9 comprises two parallel straight segments, namely a firstsegment 20 and a second segment 21, separated by an intermediate,preferably straight segment 22; the first and second segments 20, 21 areinclined by a predetermined angle to a plane perpendicular to theequatorial plane, preferably both at an identical angle “βo” ofinclination. The straight intermediate segment 22 is inclined in theopposite direction to segments 20 and 21 relative to the equatorialplane and forms an angle “γ” in the opposite direction.

[0102] The profile of the front side is the same as the profile of therear side after rotation through 180°. Preferably too, all front andrear sides of the blocks 7 of the intermediate rows and of the blocks 8of the shoulder rows are inclined by a predetermined angle to theequatorial plane and the amplitudes of the angles in one row may differfrom those of the adjacent row.

[0103] These angles are preferably equal to each other and have anamplitude “γ” (FIG. 3) which may or may not be equal to “βo”.

[0104] Advantageously, the said characteristic of inclination of thebase sides of the blocks makes it possible to present in the contactpatch a leading edge of the blocks with gradual extension as the tirecontinues to roll.

[0105] In practice, compared with patterns in which the blocks touch theground simultaneously across their full dimension, with the preferredsolution shown in FIG. 2 the ground is contacted in successive fractionsacross the front sides, which gives an advantageous attenuation of thelevel of noise produced by the impact on the ground of the leading edgesof the tread pattern.

[0106] Important characteristics of the tread according to the inventionare the widths of the central circumferential grooves 5 and of thelateral grooves 6 and also their mutual ratios and the link with thewidth of the blocks 9 of the central row.

[0107] These dimensions relate to a tread of axial width “L” (FIG. 2)defined by the shoulder edges O-O′.

[0108] The widths considered for the circumferential grooves refer tothe tread zone comprising longitudinal sides of the blocks of adjacentrows forming the walls of the circumferential grooves.

[0109] In more detail, the ratio of the width “La” of each centralcircumferential groove 5 to the width “Lo” of the blocks of the centralrow, both measured axially, is not less than 0.20.

[0110] Moreover the ratio of the width “Lb” of the circumferentiallateral groove 6 to the width “La” of the central circumferential groove5 is between 50% and 60%.

[0111] The constructional characteristic defined by the two ratiosindicated above advantageously enables large stones to be trapped in thecentral grooves 5 and smaller stones in the circumferential grooves 6,before expelling them as the tire continues to rotate.

[0112] In accordance with certain preferred illustrative embodiments,the ratios cited provide significant advantages compared with treadshaving blocks 9 in the central rows with axial width “Lo” not less than18% of the axial width “L” of the tread.

[0113] The invention includes other preferred embodiments, and morespecifically preferred predetermined amplitudes for the angle ofinclination “α” of the sides of the blocks to the equatorial plane andpreferred and predetermined values for the offset “D1” between the upperand lower sides of successive blocks in the intermediate rows.

[0114] Thus, it has been found beneficial to limit the amplitudes of theangle “α” to between 5° and 10°.

[0115] As far as the values of “D1” are concerned, values for which theadjacent “1” segments of the sides of successive blocks defining thetransverse channels 10 are between 70% and 90% of the total length ofthe sides measured between opposite vertices, have been foundbeneficial.

[0116] It has been found beneficial, for the purposes of quieter runningof the tire, to restrict the amplitudes of the angle “β” (FIG. 3) tobetween 7° and 15°, those of the angle “βo” to between 15° and 22°, andthose relating to the angle “γ” to between 30° and 60°.

[0117] The tire of the invention includes other alternative embodimentsthat are helpful in achieving good grip.

[0118] In accordance with a first embodiment the good gripcharacteristics in a tread with a total thickness “Δ” of between 21 and23 mm are related to the fact that the depth of the grooves 11 betweenblocks of the axially external shoulder row, as measured in a planeperpendicular to their centre line (FIG. 4), is equal to at least 90% ofthe thickness of the tread and the angle “η” between the walls of thegroove is not less than 22°; in a specific example of an embodiment thisangle is 26°. The width of the groove 11 is between 14 and 19 mm.

[0119] It was also considered useful, for the purposes of both furtherincreasing grip and easy removal of water, to design the transversegrooves 11 with a gradual divergence outwards away from the tire.

[0120] The opposite sides of the blocks that define the transversegrooves are preferably slightly curvilinear so as to approximate to therectilinear.

[0121] Advantageously, both the large depth and the overall dimensionsof the grooves 11 permit good ventilation of the tread in the shoulderzones, i.e. at the edges of the underlying belts whose mobility cangenerate heat in the thickness of the rubber in which they are embedded.The tread with deep grooves 11 is therefore particularly indicated forcountries with a hot climate.

[0122] In a second embodiment the shoulder rows include elastic linkagemeans between adjacent blocks 8.

[0123] These elastic linkage means consist in the fact that betweenpairs of adjacent blocks along the relevant transverse groove thereextends an elastomeric relief from the inner boundary surface of thetread towards the outer surface up to a predetermined height “h1” (FIG.6b) that is preferably between 9% and 60% of the thickness of the tread.

[0124] In one example of an embodiment in which the thickness “Δ” of thetread is 23 mm, there is a relief that increases gradually from theextremities of the groove until it reaches a maximum height “h1” of 12mm with a breadth at the maximum height varying between 23 and 28 mm.

[0125] The elastic linkage means between adjacent blocks of the shoulderrows advantageously have the effect of stiffening this row andincreasing its capacity to resist stresses.

[0126] Consequently a tire with stiffened shoulder rows can be adoptedin more stringent conditions of use than a tire with grooves 11 havingdepths greater than at least 90% of the thickness of the tread.

[0127] To further accentuate the characteristics of grip it ispreferable to adopt transverse grooves 10 (FIG. 7) having depths andangles η′ between the walls analogous to those cited earlier for thegrooves 11 of large depth.

[0128] In an example of an embodiment, the transverse groove 10 haswidths of between 13 and 16 mm and angles between the defining walls ofnot less than 22°.

[0129] In another construction the tread pattern preferably has linkagemeans between blocks lying in series relative to each other in the samecentral row 9.

[0130] In one particular embodiment these linkage means, whose purposeis to resist bending deformations, consist (FIGS. 6a, 8) in the presenceof elastomeric material between adjacent blocks of the central row.

[0131] The presence of elastomeric material is provided by anelastomeric relief extending up to a predetermined height “ho” from theinner boundary surface 3′ of the tread. In the example described, thisheight “ho” is at least 4 mm and the groove 12 immediately above it ischaracterized by the fact that, in a section perpendicular to the centreline (FIG. 8), the angle “ε” between the walls of the groove is greaterthan 20°, and still more preferably greater than 22°.

[0132] In some examples the width of the groove 12 is between 10 and 12mm and the depth is 18 mm.

[0133] In accordance with other advantageous embodiments of theinvention, the tread 3 may include stone expulsion means situatedbetween adjacent blocks defining the grooves.

[0134] In particular, these stone expulsion means comprise an anglegreater than 25° between the walls of the grooves, and a narrowing ofthe section in the vicinity of the bottom.

[0135] This narrowing of the section is preferably formed on only one ofthe two blocks defining the groove.

[0136] Although the stone expulsion means can be formed along all thegrooves, it has been found that, in a preferred embodiment, these meanscan be situated principally along the central circumferential grooves 5and in another embodiment also along the transverse grooves 12.

[0137] As regards the expulsion means along the circumferential grooves5, these consist in the fact that the aperture of the groove has anangle “δ” of not less than 24°, in one example equal to 27°, and a depthequal to at least 90% and preferably to at least 95% of the totalthickness of the tread (FIG. 5, 6).

[0138] In addition, and in accordance with this same embodiment, thestone expulsion means comprise a narrowing of the section 25 alternately(FIG. 2) on a portion of one side of the block 7 of the intermediate rowand then on one of the two lateral segments of the block 9 of thecentral row.

[0139] The narrowing of the section may be formed at a distance ofbetween 3 and 6 mm from the inner surface of the tread and may have awidth of between 2 and 4 mm.

[0140] This embodiment advantageously enables any encapsulated stones tobe expelled by the effect of the speed of rotation of the tire thanks tothe specific depth and angle of the groove; owing to the narrowing ofthe section in the vicinity of the bottom of the groove. Stones cannotpenetrate further and damage the belt layers.

[0141] Also advantageously, the provision of a narrowing of the sectionof the groove on only one side of the two adjacent blocks, incombination with the feature of multiple alternations of sectionnarrowings first on one side of one block and then on the side ofanother block, makes it possible to avoid significant removal ofelastomeric material while maintaining at optimum levels the ratiobetween the raised parts and the total volume of the tread. Thispromotes a high mileage.

[0142] In essence the advantage achieved is that of protecting the beltstructure of the tire from possible damage by the presence of stones onthe road without prejudicing the tire's grip by excessive removal ofcompound from the blocks.

[0143] Turning now to the stone expulsion means along the transversegrooves 12 of the central row, these means consist (FIG. 9) in theformation of a groove comprising an angle of aperture “k” of not lessthan 19°, in some examples between 20° and 22°, and a depth that isgenerally not less than at least 75% of the thickness of the tread, andof a narrowing 26 of the section, preferably around 9 mm deep.

[0144] In this version there are two section narrowings, one on eachside of the two adjacent central blocks.

[0145] The two section narrowings advantageously assume a triangularform in order to provide the construction of FIG. 3 with a groove ofconstant breadth suitable for uniform grip behaviour and a high capacityto drain water towards the circumferential channels.

[0146] The tire according to the invention provides many differentadvantages in addition to those indicated above.

[0147] Referring in the first place to FIG. 10, it will readily be seenthat the formation of the block 9 of the central row can be derived fromthe process of subtracting, from the area of a parallelogram with twolongitudinal sides, two transverse end sides and two diagonals S1, S2,two pairs of scalene trapezia, that is a first pair Q at the ends ofdiagonal S1, and a second pair R at the ends of diagonal S2.

[0148]FIG. 10 also clearly shows that the length of the block 9 measuredin the direction of travel W parallel to the equatorial plane reducesfrom the value T to the value To, the ratio To/T being between 0.70 and0.85.

[0149] The construction of the block 9 in relation to the polygonalshape from which it is derived offers the twin advantages of having achunkier shape and of exhibiting a notable diminution of the toe effect.

[0150] The block 9 therefore assists in making the tread stiffer andless subject to uneven wear.

[0151] Even more specifically, the shape of the blocks 9 according tothe invention is found to be beneficial when it is wished to useinclinations of the transverse end sides with angles “βo” of between 15°and 21° to the equatorial plane to obtain noise reduction.

[0152] Thus, it has been found that such angles would not be acceptablewith parallelogram-shaped blocks, unlike those of the invention, as theywould generate a large toe effect with consequent uneven wear.

[0153] A further advantage arises from the presence in the centralblocks 9 of an intermediate connecting segment, between the straightsegments inclined at an angle “γ” to the equatorial plane. This isbecause the feature of an intermediate segment inclined at angles ofbetween 30° and 60° in combination with the amplitudes of the angles “β”and “α” offers a marked discontinuity of the leading edges of the block9 with favourable results in terms of quiet running.

[0154] In practice it should be observed that the central block producedin the shape illustrated in FIG. 10 generates less noise than treadsusing blocks in which the angle “γ” approaches 0° or 90° and the angles“β” and “α” are zero. What happens is that in these possible cases theblock would present a leading edge of poor variability and so tend togenerate higher levels of noise.

[0155] Also to be pointed out is the achievement of good results inaccordance with the more general aspect of the invention owing to theshape of the blocks, in particular the shape of the central block: ascan be seen by the superimposition shown in FIG. 11, the intermediateblock 7 has an axial width and an area that are significantly less thanthose of the block 9 of the central row.

[0156]FIG. 12 clearly shows the area of the intermediate block 7 to belargely contained within the area of the shoulder block.

[0157] By comparing FIGS. 11 and 12 it can be seen that the areas of thecentral blocks are greater than those of the shoulder blocks.

[0158] The tread according to the invention therefore has blocks 9 inthe central row and blocks 7 and 8 in the intermediate and shoulder rowswhose areas differ from each other in such a way that the blocks 9 ofgreater area than the others tend to absorb greater loads, therebyprotecting the blocks 7 of the intermediate rows whose structure isweaker.

[0159] It should also be observed that the preferred embodimentcomprising elastic linkage means both between the blocks 9 of thecentral row and between the blocks 8 of the shoulder rows furtherstiffens these rows, thus protecting the blocks 7 of the intermediaterows against tearing and lacerations.

[0160] As a consequence the formation of wide central circumferentialgrooves 5 and lateral grooves 6 whose width is between 50% and 60% ofthe central grooves, while reducing the width and area of theintermediate blocks 7, does not prejudice the properties of grip andeven wear of the tread according to the invention.

[0161] It has also been found convenient to adopt the following valuesfor the axial width and area between the blocks:

[0162] ratio L1/Lo of the width of the intermediate block to the widthof the central block of between 60% and 80%; in the example shown inFIG. 11 this ratio is equal to 65%,

[0163] ratio L1/L2 of the width of the intermediate block to the widthof the shoulder block of between 80% and 95%,

[0164] ratio between the areas of the intermediate and central blocks ofbetween 60% and 75%, and

[0165] ratio between the areas of the intermediate and shoulder blocksof between 80% and 90%.

[0166] Advantageously too, the tread according to the invention offerscharacteristics of very quiet running dependent not only on the shape ofthe blocks 9 of the central rows but also on the geometricalcharacteristics of the pattern as a whole.

[0167] To demonstrate this result reference should now be made to thetread pattern indicated in FIG. 13, focusing attention on that portionthereof relating to a predetermined pitch of value “p”.

[0168] It will be observed that the characteristics of the invention aresuch that it is possible to produce a desired distance between thecentral points of the centre lines of the five transverse groovesindicated individually as r, s, t, u and v.

[0169] It will be noticed that the distance between two transversegrooves is generally around about ⅕ of “p”.

[0170] In practice it has been constructed so that from the top of thepattern and proceeding downwards the entire pitch is divided into fiveparts, all substantially defined between two lines perpendicular to theequatorial plane and separated from each other by a distance equal toapproximately ⅕ of the pitch.

[0171] Now assume that lines r, s, t, u and v correspond to successiveleading edges of the tire in the contact patch.

[0172] Notice, along each of these lines, the absence of the leadingedge of one of the blocks present in a preceding line, together the factthat in the space “p”, all five blocks belonging to the five rows of thepattern have been excluded separately from the leading edge.

[0173] The leading edge of the blocks along the contact patch thereforevaries along the five lines and since the distribution of the leadingedges along the pitch is uniform the result is uniform grip over theentire contact patch and an attenuation of the noise level owing to thedifferent succession with which the various leading edges occur over thecourse of the pitch “p”.

[0174] Another aspect tending to improve grip may also be highlighted:referring for example to the transverse grooves 10 between the blocks 7of the intermediate rows, it can be seen that there is an offset in theaxial direction between the lower and upper sides of the blocks situatedin succession in any one row.

[0175] In practice the transverse grooves of this row are defined onlyby a segment “1” (FIG. 3) of the total length of these transverse sidesof the blocks and this has the consequent advantage that it isimpossible for material such as loose or snowy material to accumulate inthe offset between the transverse sides of successive blocks.

[0176] A further advantage of the invention is due to the fact that allthe blocks of the pattern i n their many different possibleconfigurations avoid the use of edges or more generally of intersectionsof sides forming acute angles, these being shapes to which uneven wearof the elastomeric material can be attributed. As FIG. 3 shows, thesides of the various blocks form angles at the junctions ofapproximately between 80° and 110°.

[0177] Also advantageously, the pattern according to the inventionproves to be suitable for use in a tire both in the direction of travelindicated by the arrow “W” and in the opposite direction, for, as can beseen in FIGS. 2 and 3, the blocks of the lateral rows to the left of theequatorial plane rotated through 180° about their geometrical centre arethe same as the shape of the blocks of the corresponding rows to theright of the equatorial plane.

[0178] Analogously the left half of the central blocks, rotated through180°, is the same as the right half.

[0179] The present description is intended purely for explanatory,nonrestrictive purposes so that the scope of the present invention willbe understood to include also all those modifications and variations notexpressly described but readily deducible by those skilled in the artfrom the present inventive concept.

1. Vehicle wheel tire comprising a carcass structure that includes acentral crown portion and two axially opposing sidewalls terminating intwo beads for fixing the tire to a wheel rim; a belt structure coaxiallyfixed to the carcass structure; and a tread extending coaxially aroundthe belt structure and moulded to a relief pattern which comprises four,that is two lateral and two central, continuous circumferential groovesand a plurality of transverse grooves that together define at least fivecircumferential rows of blocks, that is two axially external shoulderrows, two axially internal intermediate rows and a central row thatbasically straddles the equatorial plane of the tire, each block being apolygon defined by two longitudinal sides extending in a circumferentialdirection and two transverse sides, one at the front and one at the rearwith reference to a direction of travel, characterized in that in thesaid tread pattern: a) the longitudinal sides of the blocks of each roware inclined in the same direction at a predetermined angle “α” to theequatorial plane of the tire, b) the blocks of each row arecircumferentially staggered relative to the blocks of the next row, c)the ratio of the width of each central circumferential groove to theaxial distance between the opposite longitudinal sides of the blocks ofthe central row is not less than 20%, d) the ratio of the width of eachlateral circumferential groove to the width of the centralcircumferential groove is between 45% and 60%, e) there are means ofstiffening the blocks of the central row consisting in the fact thateach transverse side of each block is formed by a first and a secondstraight lateral segments separated by an intermediate third connectingsegment, the said first and second segments being inclined to theequatorial plane, and the profile of the rear side being the same asthat of the front side rotated through 180°, and f) there are elasticmeans of circumferential linkage between the blocks of the shoulder rowsand those of the intermediate rows.
 2. Tyre according to claim 1,characterized in that the inclination of said third segment is theopposite of that of the first and second segments.
 3. Tyre according toclaim 1, characterized in that the said elastic linkage means consist inthe presence of elastomeric material of predetermined height between thebottom line of the lateral groove and the outer surface of the saidsheet.
 4. Tyre according to claim 3, characterized in that the saidpredetermined height of elastomeric material between the bottom of thegroove and the outer surface of the sheet is at least 8% of the totalthickness of the tread.
 5. Tyre according to claim 1, characterized inthat it comprises elastic linkage means between the adjacent blocks ofthe central row to contain the bending deformations.
 6. Tyre accordingto claim 1, characterized in that the said elastic linkage means consistin the fact that, between pairs of adjacent blocks along the relevanttransverse groove, an elastomeric relief extends from the internalsurface of the tread toward the outer surface up to a predeterminedheight.
 7. Tyre according to claim 6, characterized in that the saidpredetermined height is at least 15% of the thickness of the tread. 8.Tyre according to claim 1, characterized in that the said predeterminedangle “α” is between 5° and 10°.
 9. Tyre according to claim 1,characterized in that the first and second segments of both front andrear sides of the blocks of the central row are inclined in the samedirection by a predetermined angle “βo” relative to a planeperpendicular to the equatorial plane of the tire.
 10. Tyre according toclaim 1, characterized in that the said angle “βo” is between 15° and21°.
 11. Tyre according to claim 1, characterized in that the angle “γ”formed by the third intermediate segment to a plane perpendicular to theequatorial plane is between 30° and 60°.
 12. Tyre according to claim 1,characterized in that the front and rear sides of the blocks of theintermediate rows form an angle “β” to a plane perpendicular to theequatorial plane of between 70 and
 150. 13. Tyre according to claim 1,characterized in that each block of the central row is obtained bysubtracting, from the area of a polygon of essentially parallelogramshape with two transverse end sides, two longitudinal sides and twodiagonals, the areas of a first and second pairs of scalene trapezia,the two pairs being at the ends of the two diagonals.
 14. Tyre accordingto claim 1, characterized in that the ratio of the width of each centralblock to the distance between the outer edges of the shoulder rowsmeasured along a plane perpendicular to the equatorial planeintersecting the zone in which the longitudinal sides of adjacent blocksdefine the circumferential grooves is not less than 18%.
 15. Tyreaccording to claim 1, characterized in that the width of the centralblock is greater than that of the intermediate and shoulder blocks. 16.Tyre according to claim 1, characterized in that the ratio between thewidths of the intermediate block and of the central block measuredaxially in the zones in which the longitudinal sides of the blocks areadjacent is between 65% and 75%.
 17. Tyre according to claim 1,characterized in that the ratio of the area of an intermediate block tothe area of a central block is between 60% and 75%.
 18. Tyre accordingto claim 1, characterized in that it comprises elastic linkage meansbetween adjacent blocks of the shoulder rows.
 19. Tyre according toclaim 18, characterized in that the said elastic linkage means consistin the fact that, between pairs of adjacent blocks along the relevanttransverse groove, an elastomeric relief extends from the internalsurface of the tread toward the outer surface up to a predeterminedheight.
 20. Tyre according to claim 19, characterized in that the saidpredetermined height is between 9% and 60% of the thickness of thetread.
 21. Tyre according to claim 1, characterized in that the depth ofthe transverse grooves of the rows of shoulder blocks is at least 90% ofthe thickness of the tread.
 22. Tyre according to claim 1, characterizedin that the transverse grooves of the intermediate rows have a depthapproximately equal to the tread thickness.
 23. Tyre according to claim1, characterized in that in a plane orthogonal to the centre line of thetransverse grooves of the intermediate rows, the angle between the wallsof the said grooves is at least 22°.
 24. Tyre according to claim 1,characterized in that the width of the transverse grooves of theintermediate rows is between 13 and 16 mm.
 25. Tyre according to claim1, characterized in that the tread pattern repeats itself as a functionof at least one predetermined pitch, the distance between the centrelines of any two of the five transverse grooves being approximately ⅕ ofthe pitch.
 26. Tyre according to claim 1, characterized in that itcomprises stone expulsion means.
 27. Tyre according to claim 26,characterized in that the said expulsion means comprise in planesorthogonal to the centre lines of the grooves a predetermined anglebetween the walls of the said grooves and a narrowing of the section inthe vicinity of the bottom.
 28. Tyre according to claim 27,characterized in that the said predetermined angle in thecircumferential grooves is at least 24°.
 29. Tyre according to claim 26,characterized in that the said narrowing is on one side only of thegroove.
 30. Tyre according to claim 26, characterized in that the saidstone expulsion means are situated along the central circumferentialgrooves.
 31. Tyre according to claim 30, characterized in that the saidstone expulsion means comprise a narrowing of the groove on onelongitudinal side only, or alternatively a narrowing on one longitudinalside of a block in the intermediate row followed by a narrowing on theside of the block in the central row.
 32. Tyre according to claim 30,characterized in that the said stone expulsion means comprise grooveswhose depth is equal to at least 90% of the thickness of the tread. 33.Tyre according to claim 26, characterized in that the said stoneexpulsion means a re situated in the transverse grooves between theblocks of the central row.
 34. Tyre according to claim 33, characterizedin that the said stone expulsion means are situated along a transversegroove which is created by forming on each portion of two adjacentblocks two straight end segments connected by an intermediate segmentinclined to the end segments in such a way as to form an obtuse angle inan approximately central position, the said expulsion means consistingin the presence of a narrowing of the centre of the groove towards thebottom due to two opposing triangular portions.
 35. Tyre according toclaim 1, characterized in that the shapes of the blocks of the lateralrows to the left of the equatorial plane are the same as those of theblocks of the corresponding right-hand lateral rows rotated through 180°about their geometrical centres.
 36. Vehicle tire tread, the thicknessof which is defined between the outer surface intended to contact theground and the inner surface in contact with an elastomeric sheet,comprising four, that is two lateral and two central, continuouscircumferential grooves and a plurality of transverse grooves thatdefine at least five circumferential rows of blocks, that is two axiallyexternal shoulder rows, two axially internal intermediate rows and acentral row that basically straddles the equatorial plane of the tire,each block being a polygon composed of two sides extendinglongitudinally in a cicumferential direction and two transverse endsides, one at the front and one at the rear with reference to adirection of travel, in which tread: a) longitudinal sides of the blocksof each row are inclined in the same direction with a predeterminedangle “α” to the equatorial plane of the tire, b) blocks of one row arecircumferentially staggered relative to the blocks of the next row, c)the ratio of the width, measured axially, of each centralcircumferential groove to the width, measured axially, between oppositelongitudinal sides of the blocks of the central row is not less than20%, d) the ratio of the width of the lateral circumferential groove tothe width of the central circumferential groove is between 45% and 60%,e) there are means of stiffening the blocks of the central rowconsisting in the fact that each of the front and rear sides of eachblock is formed by a first and a second straight segments separated byan intermediate third connecting segment, the said first and secondsegments being inclined to the equatorial plane, and the profile of thefront side rotated through 180° being the same as that of the rear side,and f) there are circumferential elastic means of linkage between theblocks of the shoulder and intermediate rows.